Add a few warnings to the connection switcher and conf parser

[bquorning]

Mostly extracted from #136.

[grosser]

... better double-check shards in kubernetes are integers first... I'll update here once I checked

[grosser]

kk, all good!

[codebender]

This was a breaking change to the gem for everyone using strings to name the shards.

[grosser]

I think this was about sanitizing inputs ... I guess casting to int would have worked too.
Who was using strings as shards ? ... still need that ?

[codebender]

Hi @grosser,

Having named shards is really handy when you want to read/write to a specific shard that is feature specific and not "account" ID specific like in the readme.

It looks like these other people also prefer string names: #195

[grosser]

yeah sounds reasonable, can you make a PR that semi-reverts this one and allows strings ?
(change the tests to test with a mix of strings and ints)
/cc @bquorning

[holmes2]

@bquorning @grosser
Was there a reason why only integers are allowed for shard_names ?
I am trying to upgrade rails service to a higher version of this gem but still because of the shard name restriction we are not able to do it.
Is there a way to get around this shard naming restriction ?

[grosser]

I think this is because we only use it with integers and we wanted to warn our users from misconfiguration